Re: preempt-rt, NUMA and strange latency traces

Lee Revell
2006-02-09T20:02:52Z

On Thu, 2006-02-09 at 12:24 +0100, Sébastien Dugué wrote:
> On Thu, 2006-02-09 at 01:04 -0500, Lee Revell wrote:
> > On Wed, 2006-02-08 at 11:45 +0100, Sébastien Dugué wrote:
> > > The more I think about it, the more I tend to believe it's hardware
> > > related. It seems as if the CPU just hangs for ~27 ms before
> > > resuming processing.
> >
> > That would be an exceptionally long latency - you would probably notice
> > it if the mouse froze, VOIP dropped out, ping stops, etc for 30ms.
> >
>
> It's a test machine and I use it remotely with console redirected so
> no mouse, no RT applications aside from my silly nanosleep() loop. But
> I do notice that that test sometimes takes more time (ie when I get
> those weird latencies).

Argh. You would think the vendors would consider a 30ms delay
unacceptable. This is big enough to show up on an MRTG graph of ping
times ferchrissake.

I guess the assumption is that most hardware will never be used for even
soft RT work...

Lee